Charge barrier flow-through capacitor-based method of deionizing a fluid

ABSTRACT

Flow-through capacitors are provided with one or more charge barrier layers. Ions trapped in the pore volume of flow-through capacitors cause inefficiencies as these ions are expelled during the charge cycle into the purification path. A charge barrier layer holds these pore volume ions to one side of a desired flow stream, thereby increasing the efficiency with which the flow-through capacitor purifies or concentrates ions.

REFERENCE TO PRIOR APPLICATION

This application is a divisional of application Ser. No. 11/007,566,filed Dec. 8, 2004 (hereby incorporated by reference), which is acontinuation of application Ser. No. 10/772,206, filed Feb. 4, 2004(hereby incorporated by reference), which is a continuation ofapplication Ser. No. 10/015,120, filed Oct. 26, 2001; now U.S. Pat. No.6,709,560 B2, issued Mar. 23, 2004 (hereby incorporated by reference),which is a continuation-in-part of International Application No.PCT/US01/12641, filed Apr. 18, 2001, designated to be published inEnglish under PCT Article 21(2), and hereby incorporated by reference.

GOVERNMENT CONTRACT

This invention was partially funded under contract with the UnitedStates Defense, Advanced Research Projects Agency (DARPA), underContract No. DAAD 19-99-C-0033. The United States government may havecertain rights in the invention.

FIELD OF THE INVENTION

The invention relates to a flow-through capacitor for deionizing ordecontaminating a fluid.

BACKGROUND OF THE INVENTION

The invention relates to flow-through capacitors for deionizingsolutions, e.g., aqueous solutions, with improved operation atconcentrated solutions, including such applications as low energydesalination of seawater. Technologies to deionize water includeelectrodeionization and flow-through capacitors. The termelectrodeionization, including electrodialysis and continuouselectrodeionization, has traditionally referred to a process or devicethat uses electrodes to transform electronic current into ionic currentby oxidation-reduction reactions in anolyte and catholyte compartmentslocated at the anodes and cathodes. Traditionally, ionic current hasbeen used for deionization in ion-depleting compartments, and neitherthe anolyte chambers, the catholyte chambers nor the oxidation-reductionproducts have participated in the deionization process. In order toavoid contamination and to allow multiple depletion compartments betweenelectrodes, the ion-concentrating and ion-depleting compartments weregenerally separated from the anolyte and catholyte compartments. Tominimize formation of oxidation-reduction products at the electrodes,electrodeionization devices typically comprise multiple layers ofion-concentrating and ion-depleting compartments, bracketed betweenpairs of end electrodes.

One disadvantage of prior art systems is the energy loss resulting fromusing multiple compartment layers between electrodes, thereby creatingan electrical resistance. This is generally true of prior artelectrodeionization devices and is one characteristic thatdifferentiates them from flow-through capacitors.

Flow-through capacitors differ in a number of other ways fromelectrodeionization devices as well. One difference is that flow-throughcapacitors purify water without oxidation-reduction reactions. Theelectrodes electrostatically adsorb and desorb contaminants, so that theelectrode (anode and cathode) compartments participate directly indeionization and are located within one or both of the ion-depleting andion-concentrating compartments. The anolyte and catholyte are partly orlargely contained within a porous electrode. Electronic current isgenerally not transmuted by an oxidation-reduction reaction. Instead,charge is transferred by electrostatic adsorption.

However, flow-through capacitors of the prior art become energyinefficient and impractical at high ion or contaminant concentrations.The reason for this is due to the pore volume in the electrodes.Dissolved counterion salts present in the pore volume adsorb onto theelectrodes, whereas pore volume coion salts are expelled from theelectrodes. This has a doubly deleterious effect. Counterions occupycapacitance within the electrode. This amount of charge-holdingcapacitance is therefore unavailable for purification of ions from thefeed water purification stream. Coions expelled from the electrodesenter the feed water purification stream and contaminate it withadditional ions. This effect becomes worse with increased concentration.The flow-through capacitor is typically regenerated into liquid of thefeed concentration. When purifying a concentrated liquid, ions arepassively brought over into the pores prior to application of a voltageor electric current. Once voltage is applied, these ions aresimultaneously adsorbed and expelled during the purification process.Purification can only occur when an excess of feed ions, over and abovethe pore volume ions, are adsorbed by the electrodes. This puts an upperpractical limit on the economy of the flow-through capacitor, typicallyin the range of approximately 2500 to 6000 parts per million (ppm). Theflow-through capacitor of the prior art requires both slower flow ratesand higher energy usage. Beyond 6000 ppm, the energy usage required istypically more than 1 joule per coulomb of dissolved ions, making priorart flow-through capacitors too energy intensive to be practical.Seawater, which has ion concentrations of approximately 35,000 ppm,becomes impractical to deionize due to energy inefficiency caused bythese pore volume losses. Pore volume losses occur at all concentrationsbut get worse at higher concentrations. Another way to describe porevolume losses is that they cause diminished ionic efficiency. Ionicefficiency is defined as the ratio of coulombs of ions purified tocoulombs of electrons utilized.

Thus, a need exists to improve the ionic and energy efficiency offlow-through capacitors, particularly when treating solutions with ionconcentrations in excess of 2500 ppm. A further need exists for a flowthrough capacitor to purify solutions with an energy usage of less than1 Joule per Coloumb of purified ionic charge. Ionic efficiency is thecoulombs of ionic charge purified per coulombs of electrons used, andshould be 50% or more.

SUMMARY OF THE INVENTION

It has been discovered that a charge barrier placed adjacent to anelectrode of a flow-through capacitor can compensate for the pore volumelosses caused by adsorption and expulsion of pore volume ions. Using thecharge barrier flow-through capacitor of the invention, purification ofwater, such as a seawater concentrated solution, e.g., of 35,000 ppmNaCl, has been observed at an energy level of less than 1 joules percoulomb ions purified, for example, 0.5 joules per coulomb ionspurified, with an ionic efficiency of over 90%.

As used herein, the term “charge barrier” refers to a layer of materialwhich is permeable or semipermeable and is capable of holding anelectric charge. Pore ions are retained, or trapped, on the side of thecharge barrier towards which the like-charged ion, or coion, migrates.This charge barrier material may be a laminate which has a conductivelow resistance-capacitance (RC) time constant, an electrode material, ormay be a permselective, i.e., semipermeable, membrane, for example acation or anion permselective material, such as a cation exchange oranion exchange membrane. The charge barrier may have a single polarity,two polarities, or may be bipolar. Generally, a charge barrier functionsby forming a concentrated layer of ions. The effect of forming aconcentrated layer of ions is what balances out, or compensates for, thelosses ordinarily associated with pore volume ions. This effect allows alarge increase in ionic efficiency, which in turn allows energyefficient purification of concentrated fluids.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized, schematic view of a flow-through capacitor ofthe invention, illustrating the placement of charge barrier layers,electrodes, an optional current collector, and a flow channel spacer.

FIG. 2 is a generalized, schematic view of a flow-through capacitor ofthe invention, containing charge barriers of the same polarity as theadjacent or underlying electrode, together with a representation of theions being purified or concentrated, and displaying the direction of ionmigration in the electric field.

FIG. 3 represents the flow-through capacitor of FIG. 2 in the dischargecycle, illustrating the release of concentrated ions into a flow channellocated between the charge barrier layers.

FIG. 4 is a generalized, schematic view of a flow-through capacitor ofthe invention, containing charge barrier layers of opposite polarity tothat of the adjacent or underlying electrodes, together withrepresentations of ions being purified or concentrated, and displayingthe direction of ionic migration in the electric field.

FIG. 5 is a generalized view of the discharge cycle of the flow-throughcapacitor of FIG. 4, which illustrates how a centrally-located flowchannel is purified by virtue of ionic migration through the chargebarrier layers towards the electrodes.

FIG. 6 is a generalized, schematic view of a stacked-layer, flow-throughcapacitor of the invention.

FIG. 7 is a generally schematic view of a dual-flow channel,flow-through capacitor of the invention, with a sealing agent to isolatesimultaneously purified and concentrated fluid streams.

FIG. 8A is a generalized, top schematic view of the flow-throughcapacitor of the invention with transverse flow channels.

FIG. 8B is a front, cross-sectional, generalized schematic view of theflow-through capacitor of the invention with transverse flow channels.

FIG. 8C is a top sectional view of the flow-through capacitor of theinvention showing a charge barrier and a flow spacer.

FIG. 8D is a side sectional, generalized schematic view of theflow-through capacitor of the invention with transverse flow channels.

FIG. 9 shows a graph of the data generated from the flow-throughcapacitor of the invention when operated in cycles and is represented bycharging and discharging in polarities according to the sequencedepicted by FIGS. 2, 3, 4, and 5.

FIG. 10 is a generalized schematic diagram of the flow-through capacitorof the invention showing the attachment of conductive charge barriers toa separate DC power supply.

FIG. 11 is a schematic view of a flow-through capacitor system of theinvention.

FIG. 12 is a schematic view of a flow-through capacitor system of theinvention.

FIG. 13 is a schematic view of flow-through electrochemical cellsarranged in a circular stage system.

FIG. 14 is a graphical representation of a flow-through capacitorvoltage and purification cycle, showing a trace of the voltage versustime as a trace of total dissolved solids, conductivity, or percentconcentration and purification of dissolved materials versus time.

FIG. 15 illustrates a single charge barrier layer and a single flowspacer layer between two electrodes.

FIG. 16 illustrates a single layer charge barrier flow-throughcapacitor.

DETAILED DESCRIPTION

In the charge barrier flow-through capacitor of the invention, theanolyte and catholyte chambers may be integral with ion-depletion orconcentrating chambers, or they may be separate chambers. The electrodesin flow-through capacitors are spaced apart or are separated by aspacer. The spacer may be any ion-permeable,electronically-nonconductive material, including membranes and porousand nonporous materials (see U.S. Pat. No. 5,748,437, issued May 5,1998, hereby incorporated by reference). The spacer may define a flowchannel (see U.S. Pat. No. 5,547,581, issued Aug. 20, 1996, herebyincorporated by reference, or may be of a double-layer spacer materialwith the flow channel between the layers (as in U.S. Pat. No.5,748,437). Purification and concentration may take place in either thespacers, the electrodes, or both, depending upon the geometry of theflow channel. For example, in a flow-through capacitor utilizing adouble-layer spacer as described above, the ion-depleting, purification,or concentration compartment may be located between the spacer layers.U.S. Pat. No. 5,192,432, issued Mar. 9, 1993, hereby incorporated byreference, describes use of a porous electrode material. In this case,ion depletion or ion concentration would occur directly in theelectrodes themselves, in order to affect purification or concentrationof a fluid. In both cases, however, the electrodes are directly involvedin the purification process. The electrodes are used to adsorb orrelease a charge, and, generally, do not transfer electronic to ioniccurrent by oxidation-reduction reactions common to electrodeionizationtechnologies. In either case, no more than a single,separately-compartmentalized, concentrating or ion-depleting layer isrequired between each set of electrodes. Therefore, one advantage theflow-through capacitor has over deionization is that less energy iswasted by oxidation-reduction reactions and there is less internalresistance.

In the flow-through capacitor of the present invention, the chargebarrier may have just one layer or the charge barrier may have two ormore layers. Ion selective membranes may also be used to select forparticular species of ions of interest. Where the charge barrier is apermselective membrane, it may be any membrane, e.g., a nonwoven, awoven, or a semipermeable sheet material. Examples of materials for useas charge barriers are available commercially, e.g., Raipore 1010 and1030, Tokuyama Soda NEOSEPTA® CM-1 and AM-1,(NEOSEPTA® is a registeredtrademark of Tokuyarna Corporation of Mikage-cho Tokuyama City,Yamaguchi Prefecture Japan) and Selemnion brand anion and cationexchange membranes. These membranes may be supported by a web or may bemanufactured, cast, or attached integrally to the electrode material.Bipolar membranes may also be used.

Where the charge barrier material may be a low resistance multiplied bycapacitance, low resistance-capacitance (RC) time constant material,this material may be an ionically-permeable, conductive, porous, ornonporous sheet material, for example, conductive membranes, conductivepolymer sheet materials, carbon fibrous materials, either in a nonwovenor woven, e.g., woven cloth form, activated carbon cloths, nanotubes,carbon or graphite tissue, aerogel, metal mesh or fibers, perforatedgraphite or metal foil, activated carbon, and carbon black sheetmaterials, including carbons held together with apolytetrafluoroethylene (PTFE) binder. These conductive materials mayalso be derivatized with the same ionically charged groups common toanion and cation exchange membranes. It is desirable for the electrodesof the invention to have an RC time constant of less than 1000, forexample, less than 50.

Generally, any binder material used in, but not limited to, any of thepatents incorporated by reference herein, such as those binders used inelectric, double-layer capacitors, may itself be derivitized withanionic or cationic groups to form a charge barrier integratedhomogenously into an electrode.

An example of these low RC time constant, conductive charge barriermaterials is a low surface area, low capacitance, carbon black boundwith PTFE. For example, materials with a capacitance of less than 20farads/gram or 30 farads/cm² (as measured in concentrated sulfuric acid)may be used. A non-electrically conductive, ion-permeable spacer may beplaced between the electrode and the charge barrier material in order tofacilitate formation of a reverse electric field. In this case, thecharge barrier material may have integral leads, or, may have its owncurrent ion-permeable collector with leads. These leads may be hooked upin parallel with the electrode leads or may be powered by a separatepower supply. Optionally, the separate power supply may be set to avoltage that is higher than the power supply connected to theelectrodes.

In this way, the charge barrier materials contain a higher voltage thanthe electrode materials. One advantage of a discrete power supply isthat the charge barrier materials may remain permanently charged, or maybe charged to a higher voltage than the electrode materials, therebyenhancing the reverse electric field. It is this reverse electric fieldwhich forms a charge barrier to pore volume ions, thereby increasingionic efficiency of the flow-through capacitor. Alternatively, the samepower supply may be used for both the electrodes and the charge barrier.Optionally, a resistor may be added to the electrode lead circuits.

In order to further increase ionic efficiency, charge barriers mayinclude membranes, coatings, or layers with less than 10% porosity ormicroporosity. Ionic efficiency of over 70% is desirable, as defined bythe ratio of coulombs of ions absorbed to the capacitor electrodes tothe coulombs of electrodes moved through the electronic circuit into thecapacitor. Alternatively, charge barriers may have more than 10%porosity, in micro, meso, or macro pores, for example, between 10 nm and1000 micron pores. A porous charge barrier acts more like an ionexchange media that adds additional ion absorption ability to theunderlying electrodes. Porous charge barriers allow concentration ofproduct fluid during the shunt cycle in which the capacitor iselectrically discharged, reduced in voltage, or short-circuited to zerovolts. Likewise, porous charge barriers allow purification on eitherpolarity of voltage, or, offer a short concentration peak followed by apurification peak. A single layer charge barrier or porous chargebarrier flow-through capacitor, such as that shown in FIG. 15, or,double-layer charge barrier cells, may sometimes show deeperpurification and more concentrated concentration every other chargecycle of like polarity.

In these cases, it may be advantageous to save the product fluid fromrelatively less purified cycles, or portions of cycles, particularlywithin the beginning and end one-third of a particular cycle, in orderto feed this back into the alternate cycles which produce the morepurified or more concentrated product water. The reverse of the above,feeding more purified cycle into a less purified cycle, may also bedone. A conductivity sensor, timer, or counting means may select waterfrom particular cycles by triggering a three-way valve once waterconductivity climbs above a conductivity set point and by use of thisvalve, direct this flow to an accumulation tank, bladder tank, or inseries flow through another flow-through capacitor. Single or multiplecycles may be pooled together this way. Where purification cyclesalternate as above, this partly purified water may be directed to thealternate cycle in the same or in another capacitor, which produces thehigher degree of purification. Four or more capacitors may be used tocombine series flow with staggered purification and concentration cyclesin order to achieve a continuous product of over 50% purified, forexample, over 95% purified, and continuous wastewater flow concentratedover 50% concentrated. A minimum of two flow-through capacitors isrequired in order to provide staggered continuous purification andconcentration cycles. Purification cycles are relative to each other orto the feed water concentration or conductivity.

Any electrode material suitable for use in a flow-through capacitor maybe used as the underlying electrode material for the present invention.For example, small particle size carbons have lower series resistance.Carbon particles of less than 10 microns, for example, 1 micron or less,may be formed into an electrode sheet with PTFE or other binders andcalendered or extruded into sheet electrodes of less than 0.02 inchesthick with low series resistance, e.g., less than 40 ohm cm², where cm²is the spacer area.

The charge barrier material may preferably be combined with theelectrode. In this way, the electrode itself offers structure andstrength, so that a thin, weak charge barrier may be used. For example,a thin coating of a charge barrier ion exchange material may be applieddirectly onto the electrode. Alternatively, the charge barrier materialmay be directly infiltrated into the electrode, especially if theelectrode is porous or provided with holes as exemplified in U.S. Pat.No. 6,214,204 (hereby incorporated by reference). A preferred embodimentis to provide a carbon electrode with a secondary pore structure that islarger than the primary surface area pores. These large secondary poresmay be coated with or infiltrated with an anion or cation exchangematerial. Since the electrodes provide strength, the ion exchange groupson the charge barrier material may be supported on a hydrogel, forexample polyacrylamide or polysaccharide material. Suitable ion exchangemembrane formulations and ionic groups may include, for example,perfluorinated films, NAFION™, carboxylate or sulfonate polymers,perfluorinated sufonic acid, a mixture of styrene and divinylbenzene,olefins and polyolefins, or any polymer derivatized with various ionicgroups, including sulfonyl halide, amine, diamine, aminated polysulfone,carboxyl, sulfate, nitrate, phosphate, chelating agent,ethylenediaminetetraacetic acid (EDTA), cyanide, imine,polyethyleneimine, amide, polysulfone, or any other fixed ionic groupmay be used as the charge barrier material. See also, Thomas A. Davis etal, A First Course In Ion Permeable Membranes (The ElectrochemicalConsultancy, Hants, England, 1997).

Another preferred embodiment of the present invention is to combine thecharge barrier within the structure of the electrode. Any electrodematerial that has through holes, or which has a porous structure, may beused. The porous structure may include a combination of pore sizes, forexample, macropores, micron-sized pores or larger, combined with meso ormicro pores in order to improve conductivity of ions into the electrodeand accessibility of the surface area. The charge barrier material maybe infiltrated into this pore structure in order to form a combinedelectrode-charge barrier material that may be used as spaced-apartelectrodes or with any flow spacer.

For use in the present invention, capacitor electrodes, electrodeproperties, spacers, material properties, and methods of manufacturewill be known to those skilled in the art. For example, guidance isprovided in connection with carbon double-layer capacitors, includingbut not limited to the following documents, each of which is herebyincorporated by reference: U.S. Pat. Nos. 5,558,753, issued Sep. 24,1996; 5,706,165, issued Jan. 6, 1998; 5,776,384, issued Jul. 7, 1998;6,094,788, issued Aug. 1, 2000. See also, PCT International ApplicationNos. WO 98/15962, published 16 Apr. 1998; and WO 01/45121 A1, published21 Jun. 2001; and EP Patent No. 0 436 436 B1, published 17 Aug. 1994.

With the addition of charge barrier layers and flow paths, any electrodegeometry of capacitor housing or cartridge ordinarily used indouble-layer capacitors, including but not limited to the above, may beused to make a flow-through capacitor of the present invention. Flowpaths may be formed by creation of inlets and outlets through capacitorhousings, including but not limited to those referenced herein, while atthe same time sealing capacitor layers against the housing to directfluid flow through or across the layers of capacitor materials, and toprevent fluid channeling around, over, or under the layers of capacitormaterials.

Systems designed for the charge barrier flow-through capacitor, or forflow-through capacitors generally, may be any design used inelectrodialysis, ion exchange, or reverse osmosis, including but notlimited to U.S. Pat. No. 5,558,753, issued Sep. 24, 1996, which ishereby incorporated by reference.

As mentioned previously, extra purification compartments increaseelectro-static resistance (ESR) and increase energy usage. However,especially when combined with energy recovery, an additional embodimentof the present invention would be to include multiple ion-depleting andion-concentrating compartments between the capacitor electrodes. Unlikeelectrodialysis, the end electrodes would still participate in iondepletion or concentration to the extent that they adsorb or desorbions. The major improvement of such a device over electrodialysis wouldbe the opportunity to recover energy from the capacitor electrodes.These multiple compartments would consist of multiple pairs, from two toone hundred or more, of like or oppositely charged ion-exchangemembranes or charge barriers separated by a flow spacer. These chargebarrier pairs would be placed between capacitance-containing electrodes.Alternating ion-depletion or concentration channels could be gasketedusing any means common to electrodialysis or electrodeionization.

FIG. 1 shows a generalized drawing of a charge barrier flow-throughcapacitor, with electrode 2, charge barrier 3, spacer 4, and optionally,current collector 1. An electrode 2 is prepared from a high capacitancematerial, preferably with a capacitance of over 1 farad per gram or 1farad per cubic centimeter (as measured in concentrated sulfuric acid).The charge barrier 3 may be a permselective membrane of either polarityand either the same polarity as each other or an opposite polarity. Thecharge barrier 3 may also be a bipolar membrane. The charge barrier 3may also be prepared from an electrode material with a lower RC timeconstant than the underlying electrode 2, and either laminated duringmanufacture directly upon and integral to electrode 2, or simply laidtogether separately. For the best results, the electrode material shouldhave an RC time constant that is at least twice as high as the RC timeconstant of the charge barrier 3. In order to improve performance of thecharge barrier 3, the capacitance of the underlying electrode may bereduced or resistance of the underlying electrode 2 may be increasedrelative to the charge barrier 3 material. Ideally, the electrode 2 RCtime constant may be manipulated by increasing capacitance more than byincreasing resistance, in order to have a low series resistance, highlyenergy efficient capacitor. So that the charge barrier 3 may have alower RC time constant than the underlying electrode 2, eitherresistance or capacitance of the charge barrier 3 may be decreasedrelative to the electrode 2. However, changing either value will sufficeto alter the RC time constant. During charge of such a laminatedelectrode 2, with the lower RC time constant material facing outward tothe flow channel spacer, the outer low RC time constant electrode 2charges up first. This creates an inverse electric field localizedwithin the electrode 2 of the opposite direction to the electric fieldbetween the anode and cathode electrodes 2. This inverse field holdspore volume ions trapped within the electrode 2.

In order to maintain charge neutrality, counterions migrate into theelectrode 2 where they form a concentrated solution with the trappedcoions, thereby increasing ionic efficiency. Generally, spacer 4 may beprepared from any material which defines a flow channel, or it may besimply a space between the anode and cathode pairs of electrodes 2 thatis ionically permeable and electron insulating, with flow channel 5defined by the spacer 4, within the spacer 4, or in the layers betweenthe spacer 4 and the electrode 2. This flow channel 5 may be formed bygrooves or ribs embossed into either the spacer 4 or electrode 2.Alternatively, the spacer 4 may be an open netting, filter, particulate,or screen-printed material of any geometry that serves to space apartthe electrode 2 layers and allow flow paths 5. The spacer 4 may be adoubled-up layer of material with a flow path 5 between the layers. Itis desirable that the flow spacer 4 be thin, e.g., under 0.01 inchesthick. Further, it is desirable that doubled-up charge permselectivemembranes or membranes and flow spacer combinations be thin, e.g., under0.02 inches thick, and preferably, less than 0.01 inch thick. If thecharge barrier 3 is a permselective membrane, the polarities may be thesame, either negative or positive, or there may be one of each polarity,i.e., one negative and one positive. In order to limit seriesresistance, the electrodes 2 should also be thin, such as under 0.06inch thick, for example, 0.02 inch thick or less. Spacing between layersshould also be thin, such as under 0.06 inch, for example, 0.01 inchesor less. It is important to limit leakage, because this bleeds off thecharge responsible for maintaining a charge barrier.

Leakage resistance of over 100 ohm cm² is preferred, such as over 1000ohm cm², and series resistance of under 50 ohm cm² is preferred, asmeasured by recording the instantaneous current upon application of 1volt to a cell equilibrated with 0.1 M NaCl. The cm² in the ohm cm²above refers to the electrode 2 facing area, which is the same as thespacer 4 area. The ratio of leakage resistance to series resistanceshould be in excess of 100, such as, for example, in excess of 300.

Electrode 2 materials may be selected for nonfouling characteristics.For example, activated carbon tends to absorb organics and many ionspassively. Carbon blacks, which may be selected for use, show lesstendency to adsorb passively a foulant that is causing a problem withactivated carbon electrodes 2. Carbon black may also be derivatized withfluorine groups in order to make it less passively adsorptive. However,for treatment of polyaromatic hydrocarbons, trihalomethane, and otherorganics, the passive absorptive behavior may be selected for inelectrode 2. These electrode 2 materials may be electrochemicallydestroyed once they are adsorbed passively. To facilitate passiveadsorption, it may be advantageous to provide flow pores through thecurrent collector 1 and electrode 2 so that nonionic species may beexposed to the electrodes 2 by convective flow there through. Chargebarrier 3 material may also be a permselective membrane, such as acation, anion, or ion-specific membrane material.

Flow-through capacitors of the invention may be electrically connectedin series as separate, electrically-insulated cells. These cells may bebuilt within the same flat stacked layer or within a spirally-woundlayer, flow-through capacitor. For example, individual cells containingmultiple electrode pairs and other layers may be provided with anionically-insulating component on the end of the electrode 2 stack. Thisionically-insulating component may be electrically conductive so as toform an electrical series connection from one capacitive layer to thenext, on opposing sides of this ionically-insulating layer. A number ofcells may be rolled up in concentric spirals in order to form anelectrical series, connected, flow-through capacitor with parallel fluidflow between the layers. A cell is any arrangement of layers thatincludes parallel pairs of electrodes 2 with the same voltage. Bystacking cells in series, the voltage is additive across the stack andis therefore increased in order to take advantage of less expensive,higher voltage, lower amperage power. For example, a 480 to 600 voltstack is ideal for use with power received directly from transmissionlines, without the need for transformers to step down the voltage.

FIG. 2 represents a flow-through capacitor of the inventionincorporating electrode 2 and charge barrier 3. In this case, the chargebarrier 3 either has a lower RC time constant material than doeselectrode 2, or the charge barrier 3 is a permselective membrane of thesame polarity as the adjacent electrode 2. Upon applying voltage, anionsand cations are expelled from the anodes and cathodes, respectively. Theion movement is shown in FIG. 2 by the horizontal or bent arrows. Theseions are repelled by and trapped, against charge barrier 3, which, ifmade from a low RC time constant material, has like polarities in theform of electric charges, or, in the case of a permselective membrane,has like polarities in the form of bound charges to that of the adjacentelectrode 2. Ions from the flow channel 5, e.g., a central flow channel,migrate through the permselective membrane to balance the charge ofthese trapped ions. As a result, a concentrated solution of ions formsin the compartments surrounding electrode 2. Ions are depleted from theflow channel 5, allowing purified water to exit the flow channel 5.Counterions already present in the pore volume electrostatically adsorbon their respective electrodes 2. Although, this takes up an adsorptionsite, the concentrated solution formed by the trapped ions and by thecharge-balancing ions make up for any loss of adsorption capacity.

In essence, the charge barrier 3 forms an inverse electric field, whichkeeps coions inside the electrode 2. In order to balance charge,counterions migrate into the electrode chamber where they form aconcentrated solution, thereby, allowing a flow-through capacitor ofimproved ionic efficiency, e.g., such as 30 to 99%.

FIG. 3 represents the flow-through capacitor of FIG. 2 after it isdischarged. Desorbed ions, together with ions that had concentrated inthe electrodes 2, are discharged as a concentrate. A flow channel 5 maybe formed from a spacer component (not shown). Spacer 4 may be formedfrom flow patterns directly embossed into the electrode 2 or from aseparate flow channel 5 forming spacer 4 (shown in FIG. 1), such as,without limitation, an open netting material, screen-printed protrusionsor ribs, or a nonwoven filter material.

Spacer 4 may be incorporated into one or more flow channels 5. Flowchannel 5 may exist as two types, i.e., between the charge barrier 3layers or between the electrodes 2 and charge barriers 3, or both typesof flow channels 5 may exist at the same time, with each type isolatedfrom the other type. Two simultaneous types of flow channels 5 allow forsimultaneous purification and concentration.

FIG. 4 represents a flow-through capacitor with a double permselectivemembrane adjacent to the electrode 2, whereby the adjacent membranes areof opposite polarity to the electrode 2. This may be accomplishedelectronically, merely by reversing the polarity of the capacitor inFIG. 2, for example, if operating the capacitor with alternatingpolarity charge cycles. In the capacitor of FIG. 4, ions concentrateinto the space between the membranes during application of a voltage.Flow channels 5 may be incorporated centrally, or two-sided, or bothside and central. A concentrate is released from the central flowchannel 5 during application of a voltage. If the side and central flowchannels 5 are isolated by a gasket or sealing agent, then purifiedwater may be retrieved from the side flow channels 5 at the same timethat concentrated water is retrieved from the central flow channel 5.

In FIG. 5, purified water is collected from the central flow channel 5.This mechanism is due to the fact that the discharging capacitor of FIG.4, with opposite-charged permselective membranes adjacent to theelectrodes 2, is analogous to the charging capacitor of FIG. 2, withlike-charged permselective electrodes 2 adjacent to the electrodes 2.When the capacitor of FIG. 4 is discharged, an interesting observationmay be made, discharging counterions become trapped between theelectrode 2 and the membranes, where they draw ions from the centralchannel into the side channels in order to maintain electroneutrality.If isolated side flow channels 5 were also provided, concentrated fluidmay simultaneously be retrieved.

By incorporating a separate flow channel 5 shown in FIGS. 2 and 4, theflow-through capacitor purifies and concentrates simultaneously. Theflow-through capacitor of the invention may also have a central flowchannel 5 composed of opposite or like-polarity permselective membranes.In the case of opposite-polarity membranes, the flow-through capacitormay be cycled with alternating-charge polarities. This situation isrepresented by the charge polarity shown in FIG. 4, followed by thedischarge cycle shown in FIG. 5, followed by the polarity shown in FIG.2 (the reverse of FIG. 4), followed by a discharge cycle. This situationcreates two purification cycles in a row, followed by two concentrationcycles in a row. Therefore, the flow-through capacitor of the inventionmay extend artificially the length of time the cell spends purifying.Depending upon the orientation of the membranes, purification orconcentration can occur either upon a voltage rise or a voltagedecrease. This differs markedly from flow-through capacitors of theprior art, which exhibit purification upon application of voltage ofeither polarity, as opposed to a change in voltage, for example, fromnegative towards zero.

FIG. 6 shows a stacked-layer capacitor of the invention. Material layersare arranged around a central flow hole 8. Material layers may be discs,squares, or polygons consisting of electrodes 2, charge barriers 3materials (either lower RC time constant electrode 2 material orpermselective membranes of the same or opposite polarities). Optionally,spacer 4 forms a central flow path 8. The spacer 4 may be prepared from,for example, any open netting, nonwoven cloth, loosely applied particlematerial, screen-printed protrusions, or ribs.

FIG. 7 shows a layer capacitor of the invention modified so as to allowmultiple flow paths 5. Charge barriers 3 are prepared with permselectivemembranes. Permselective membrane 3 are sealed to electrode 2 in orderto form two alternating flow paths. One flow path 24 flows between pairsof permselective membranes and out flow holes 26. The other flow path 25flows between electrode 2 and one charge barrier 3, and then out throughseparate flow holes 27. This capacitor has two discrete outlets formedby the seals 9 but does not require inlets to be separately sealed.Optionally, the inlets may be separately sealed in order to allowbackwashing. The seal 9 may be accomplished by using, for example, awasher, gasket, glue, or resin material that seals layers together.Optionally, the electrode 2 may have an enlarged central hole 10 so thata seal need only be made between two charge barriers 3, rather thanbetween a charge barrier 3 and an electrode 2. The layers of chargebarriers 3 and electrodes 2 may be repeated within a particular cell anynumber of times. Typically, where the electrode 2 is an end electrode,it may be single-sided; whereas, where the electrode 2 is internal, itmay be double-sided, such as on either side of a current collector 1within the same cell.

FIGS. 8A, 8B, 8C and 8D represent a flow-through capacitor of theinvention comprised of parallel rectangular layers of electrodes 2, aspacer 4, e.g., a flow spacer to allow an electronically-insulated flowchannel 5, located between an electrode 2 and a seal 9, e.g., a gasketseal to form two sets of isolated, manifolded flow channels 5. Thecharge barrier 3 may function as, or together with, the seal 9 gasket. Aflow slot 10 may be cut into one end of charge barrier 3. This forms amanifold flow channel 23 between two layers of charge barrier 3. Aspacer 4, shown in the inset, may be placed between the charge barrierlayers 3 in order to form a flow channel 5. Containment plate 11 is partof a cartridge holder that holds the entire flow-through capacitorcartridge formed of the layers of charge barrier 3. A second set of flowchannels 5, transverse to the above flow channels 5, is formed betweenelectrode 2 and charge barrier 3. These flow channels 5 may be formedfrom another set of spacers (not shown) located in this space or may beformed from a textured pattern embossed directly into either theelectrode 2 or charge barrier 3. A flow channel 5 may be formed from anetting, a ribbed particulate, a microprotrusion, or a diamond-shapedpattern, e.g., a protruding or embossed pattern to form a flow channel5. Any of the layers may contain a flow channel 5 or may be textured, orhave openings, pores, or spacers to form a flow channel 5. The flowpattern may, for example, consist of 0.001 inch deep grooves in apattern of 0.005 inch diamonds embossed in a 0.01 inch thick electrode2. These transverse flow channels 5 are likewise manifolded togetherinto common inlets and outlets. In this way, simultaneously-concentratedand purified fluid streams may be fed into or collected from theflow-through capacitor.

FIG. 9 shows a graph of the data obtained from a capacitor charged inthe sequence demonstrated by charging as shown in FIG. 2, discharging asshown in FIG. 3, with the polarity of electrode 2 set so as to charge asshown in FIG. 4, and followed by discharging as in FIG. 5. Note how inthis case, purification occurs upon a voltage rise, and concentrationoccurs upon a voltage decrease.

FIG. 10 represents an arrangement of layers of charge barriers 3 in theflow-through capacitor of the invention where the charge barrier 3 is aconductive material having a lower RC time constant than the electrode2. The ratio of RC time constants of charge barrier 3 to electrode 2should be more than a factor of two, and preferably, more than 4, suchas, for example, 10.c

Electrode 2 is connected by lead 12 to DC power source 13. The lead 12may be integral with the electrode 2 or may be attached to a separatecurrent collector layer (not shown), in which case the electrode 2 maybe on both sides of the current collector. A spacer 4, such as anionically-conductive, electrically-insulating spacer or a flow spacerseparates the electrode 2 from the conductive, low RC time constantcharge barrier 3. A separate power source 14 connects through its lead12 to the charge barrier 3 in order to charge the charge barrier 3 to ahigher, varying, or constant voltage than the underlying electrode 2. By“underlying” is meant in the direction of migration of cation 6 andanion 7. The anion 7 is held inside the chamber containing left,negative electrode 2 and spacer 4. This causes a cation 6 to migratethrough the charge barrier layer 3, where it forms a concentratedsolution in conjunction with anion 7. The opposite occurs on the otherside of the flow-through capacitor.

FIG. 11 represents a stack of flow-through capacitors 15 with separatepurification and concentration streams. Flow-through capacitors 15 arefluidly and electrically connected with leads 12 in series. The DC powersource 13 provides the voltage and selected constant or variable currentto the capacitor 15 stack. The controller, logic, and switchinginstrument 20 provides alternating-polarity charge cycles and dischargecycles. Conductivity controller 22 monitors the outlet fluidconcentration of purification stream 18 to provide data with which tooperate logic instrument 20, and valve component 16, which switch fluidstreams in order to separate waste stream 17 and purification stream 18.Optionally, the hold-up tank 21 regulates the flow in case purificationstream 18 is variable or intermittent. Optionally, a component 19 may beplaced upstream of the capacitors 15 to pretreat the water. A component19, may be any technology known to treat water, for example, a componentfor reverse osmosis, micro or ultra filtration, carbon filtration,flocculation, electrowinning, or addition of chemicals. For example, itmay be desirable to add chemicals that will presterilize the water,which chemicals may be further reduced or oxidized to a salt form byfurther chemical addition, then removed later in their salt form fromthe flow-through capacitor 15. A pretreatment component 19 may also beused for a post treatment, by placing it downstream of the flow-throughcapacitor in the outlet purification stream 18.

FIG. 12 is a schematic view of a flow-through capacitor system of theinvention including: conductivity sensor and/or controller 31; feedstream 32; product water 33; wastewater 34; water recycle loop 35; cellbypass streams 36; individual cell feed or wash streams 37; pump 38;flow or pressure control and/or sensor means 39; relays 41; logic means42; flow-through capacitor one 43; flow-through capacitor two 44;flow-through capacitor three 45; flow-through capacitor four 46; feedback valves 47; energy recovery circuit 48; power supply 49; three-wayvalve 101; three-way valve 102; three-way valve 103; three-way valve104; three-way valve 105; three-way valve 106; three-way valve 107;three-way valve 108; three-way valve 109; three-way valve 110; three-wayvalve 111; three-way valve 112; and three-way valve 113.

Feed stream 32 is pumped via pump 38 and optional flow or pressurecontroller 39 into any one or any combination of flow-through capacitors43, 44, 45, and 46, either one at a time, in parallel, or in seriesflow. The number of capacitors may be any number, for example, two totwo hundred. Valves, shown here as 101, 102, 103, 104, 105, 106, 107,108, 109, 110, 111, 112, 113, work singly, together, or in combinationto allow feed water to flow-through individual cells or through groupsof cells, either in parallel or series flow. Alternatively, the valvesmay be pairs of three-way valves between each cell, or alternatively,may be replaced by any combination of two, three, four, five, or six-way(or more) valves. Preferably, a valve arrangement or combination is usedthat allows a particular capacitor or “cell,” to be bypassed, thatdirects purified water and concentrated water in different directions,or that allows fluid from one cell or from a group of cells to be fedinto any other cell or group of cells. Valves are used to select betweenthe feed stream and the waste stream, to take a capacitor out of serviceentirely, or to feed the flow from one capacitor into another.

The system of FIG. 12 is versatile, in that at any one time, differentcells may be purifying and/or concentrating waste. Therefore, continuousproduct and waste streams may be obtained. One or more conductivitysensors or controllers can be placed in the path of a fluid stream, inorder to send a signal to logic means 42. Logic means 42 may controlrelays 41, so as to in turn switch polarity in particular capacitors,shunt, or charge. A capacitor may be discharged through energy recoverycircuit 48, and optionally, used to charge another capacitor in order torecover the energy. Energy recovery circuit 48 may contain one or moreinductor coils or may contain a DC to DC converter.

Conductivity sensor 31 can measure product water and switch waterfeedback valves to recycle product or wastewater through water feedbackloop 35 back into the feed stream.

By recycling water in such a manner, substandard water can be selectedfor a conductivity sensor or timer means and fed back into the capacitorin order to minimize wastewater, minimize energy usage, and to obtain abetter average product water. For example, a water quality cut off of50% purity or better may be programmed into logic means 42 regulated byconductivity sensor 31 measurement of product water. This can be used torecycle the flow at either/or both of the beginning and the end of apurification cycle, each of which tend to be of less quality than themiddle of the cycle. A timer may also suffice to select the end andbeginning of a purification cycle, for example, to recycle the first andlast one-third or less.

Valves 47 and 102 through 113 are optional, or may be replaced bycombinations of two-way and check valves.

Logic means 42 may regulate charge and discharge cycles such that aseries stack of flow-through capacitors as shown in FIG. 12 may operatewithout bypass streams 37, individual cell feed streams 36, or anyintermediate valves 101 through 113. Bypass loop 35 and valves 47 arealso optional. For operation without intermediate valves, a segment ofpurified water is flushed through successive capacitors in series flow.Flow rate is synchronized so that, as a segment of partially purifiedwater reaches each successive capacitor, that capacitor's purificationcycle or cycles are triggered. Therefore, each time a segment ofpartially purified-water travels through another capacitor in seriesflow, it is purified more. This segment of purified water is followed bya segment of wastewater. Each time this segment of wastewater travelsthrough a capacitor, that capacitor's concentration cycle or cycles aretriggered, thereby further concentrating the waste stream as it travelsthrough each successive capacitor. In this way, purification andconcentration segments are resolved. These can be separated as they exitthe last capacitor by a conductivity sensor means 31 which actuates athree-way valve that discharges waste one way and purified water anotherway, based upon preselected product and wastewater cut-offconcentrations, for example, more than 50% purified product or more than50% concentrated waste.

FIG. 13 is a schematic view of flow-through electrochemical cellsarranged in a circular stage system, including: flow-through capacitorsor electrochemical cells 49, 50, 51, and 52; two, three, or four-wayvalves 114,115, 116, 117, 118, 119, 120, 121, 122, 123, 124, and 125 andmanifold or valve 126.

FIG. 13 depicts a circular stage system for charge barriers inflow-through electrochemical cells, such as flow-through capacitors.Although, the system shown has four cells, it may include more cells andsimilar valves between the cells in order to have any number of cellsfrom two or three cells to a hundred cells or more. The number ofpossible cycles are generally as many as the number of cells in thecircle.

FIG. 13 depicts a four-cell system with cells 49, 50, 51, and 52, andemploying four cycles. Cycle 1 is a concentration cycle, wherein theflow path is directed through cells 51 and 52 using manifold 126 andvalves 120, 122, 123, and 125, with valve 121 selecting the concentratestream to a common concentrate stream with the other cycles. Valves 115,116, 117, and 119 direct flow-through cells 49 and 50 during theirpurification cycle, with the purified stream selected to a common pathwith subsequent cycles using valve 114.

Likewise, in cycle 2, valve combinations 115, 116, 123, 124, 125 and117, 118, 119, 120, 122 are used. In cycle 3, valve combinations 120,121, 122, 123 & 125 and 114, 115, 116, 117, and 119 are used. In cycle4, valve combinations 114, 115, 116, 117, 119 and 117, 118, 119, 120,and 122 are used. These valves may be three-way valves, may be largelyor entirely subtracted from the system, or may be replaced with four,five, or six-way or higher valves. Single valves, pairs, triplets, ormultiples of two or three-way valves, or two-way valves combined withcheck valves, may also be used between each cell. It is especiallydesirable, in any flow-through capacitor system to recirculate slightlypurified water from either the product stream, or the waste stream, orfrom any capacitor outlet streams, back into a capacitor inlet stream orback into the feed stream.

Concentrated waste may be recycled in order to reduce wastewater volume,for example, to less than 50% wastewater at over 50% concentrate. BothFIGS. 12 and 13 allow for continuous purification and concentration.Flows of feed, purified, or concentrated solution may flow sequentiallyor in parallel through capacitors. Capacitors may be connectedelectrically in series or in parallel. In the systems of FIGS. 12 and13, it is possible to program or allocate a lesser proportion of time ina particular cell for concentration than for purification or vice versa.Optionally, more than one group of cells can form a continuouspurification/concentration cycle at once.

Conductivity sensors are located at the feed, input, or output of any orall of the cells shown in FIG. 12 or 13. The conductivity sensormeasures the input or output of a given cell. This sensor may determinewhen the output fluid quality has deteriorated beyond a programmed setpoint, or as a percentage of the input or feed, for example, outputconcentration is some number less than 99% compared to feedconcentration. Once a set point has been reached, a signal is sent tologic means 42, which in turn activates any combination of valves 47,and 100-103, shown in FIG. 12 or sets of valves, in order to flush,remove cells from the flow path, and relays to reverse polarity or shunta particular cell or set of cells. For example, a particular cell orgroup of cells can be removed from the purification flow path whilebeing flushed with feed water in order to discharge concentrated waste.For example, valves 101 and 103 control cell 44 and can either remove itfrom the flow path, flush the waste into the waste stream, or directpurified water to the product stream, to an accumulation tank, or to asubsequent cell for further stages of purification. Valves 102, 103,104, and 105 perform the same function for cell 44, shown in FIG. 12.Likewise, valves 106, 107, 108 and 109 perform this function for cell45, and valves 110, 111, 112, and 113 for cell 46. The temporarilyclosed flow path between valves 125-115 and 120-119 is not shown.

FIG. 14 is a graphical representation of a flow-through capacitorvoltage and purification cycle, showing a trace of the voltage versustime 54 as a trace of total dissolved solids, conductivity, or percentconcentration and purification of dissolved materials versus time 55.

FIG. 14 depicts a voltage cycle where voltage does not remain at thezero voltage point (as it does in FIG. 9). The correspondingpurification and concentration cycles are also shown. These lattercycles may be between 0 and 360 degrees out of phase with the voltagecycles. Moreover, the decreasing voltage may be faster, or slower, orexhibit a different shape of curve or slope of line than the increasingvoltage part of a particular cycle, e.g., zigzag, square, constantlyaccelerating, and irregular voltage patterns are possible.

FIG. 15 illustrates a single charge barrier layer and a single flowspacer layer between two electrodes.

FIG. 16 illustrates a single layer charge barrier flow-through capacitorincluding: optional current collector 1; electrode 2; charge barriermaterial 3; flow spacer 4; flow channel 5; and an optional layer ofelectrically and ionically-insulating sheet material 53 to form seriescells.

FIG. 16 depicts a flow-through capacitor having a single-layer chargebarrier. The charge barrier material 3 can be any ion-selective orion-exchange material. The charge barrier material may also be achelating material with preference for particular metals. For example,the charge barrier can be a layer of loose or bound togetherion-exchange particles, resin, or beads, between two layers of electrodematerial. The charge barrier may be a homogeneous or heterogeneousion-exchange sheet material or, e.g., a material with either positive,negative, amphoteric, chelating, or mixtures of the above groups willserve for purposes of the invention. A preferred embodiment is anion-exchange material with an ion-exchange capacity of over 0.01milliequivalents per gram of material, for example, over onemilliequivalent of ion-exchange capacity per gram of charge barriermaterial or higher. A material in the 0.01-0.2 milliequivalents per gramrange may be suitable as well.

In a preferred embodiment of the invention, the charge barrier materialhas low resistance, decreasing series resistance losses to less than 30%of total energy losses. Charge barrier material resistance of under tenohm cm², preferably under 3 ohm cm², is particularly desirable, forexample, one ohm cm² or less. Gel water percent of less than 50% is alsodesirable. To achieve a low resistance, thin charge barrier materialsmay be used, for example, less than 0.020 inches thick, for example,0.005 inches thick or less. Polymer materials may be applied directlyonto carbon electrodes and cross-linked in place with sufficient amountof cross-linker and subsequently derivitized with ion-exchange groups inorder to achieve similar properties to the above. Charge barriermaterials may be a membrane, a coating, a cross-linked polymer, any ofthe above homogenously infiltrated into a porous electrode, or into thelarger pores of a mixed pore size material. The charge barrier materialmay be a polyelectrolyte, hydrogel, ionomer, or membrane. Examplesinclude methacrylic or acrylic acid with over 1% cross-linking,perflourosulfonate membranes such as Dupont NAFION™, a copolymer ofstyrene with, without limitation, polyvinylidene fluoride (PDVF),fluorinated ethylene-propylene (FEP), PTFE, polyolefin, orpolypropylene, with the styrene groups derivitzed with ion-exchangegroups, such as, e.g., sulfate or tertiary amines. A nonwoven materialderivitized with ion-exchange groups is also suitable. Alternatively,the carbon of the material can be derivitized directly with ion-exchangegroups to integrate the charge barrier properties with the electrode.Electrodes so derivitized may use additional charge barrier layers ofany of the above-mentioned materials. Derivitization of carbonelectrodes, for example, to have an ion-exchange capacity, either anion,cation, or both, of over 0.1 milliequivalent per gram, increasesperformance of the electrodes when used together with single or doublelayers of any other additional charge barrier materials.

Introduction of fluid from one cell to the next may be delayed or laggedby deliberate introduction of a lag or dead volume between cells. A lagvolume of 1% or greater of a given purification cycle's volume, asmeasured by flow rate times cycle time, will be useful for this purpose.A conductivity sensor may trigger a subsequent cell's purification orconcentration cycle once it is detected that the purified orconcentrated stream from the previous cell has begun to exit the secondcell. In this way, a particular cell's purification or concentrationcurve may be centered in the subsequent cell when the next purificationor concentration cycle is initiated. Purification or concentrationcycles may be two upward or downward voltage events, or may be a singleupward or downward voltage event. Direction or rate of change of voltagemay be adjusted, moved forward or backward in time, or shortened orlengthened in time, so that a slug of purified or concentrated watermoves through successive cells with synchronous purification orconcentration events, in order to purify or concentrate in stages.Closed-loop feedback control with a signal from a fluid conductivitysensor can be used to regulate and adjust voltage cycles so as tosynchronize staged cells.

It may be desirable to run pairs or groups of cells at charging ordischarging voltages that are out of phase, for example, between 0 and180 degrees of phase. In addition, it may be desirable to introduce flowfrom one cell to another out of phase. For example, it may be desirableto introduce fluid from a subsequent cell one or more seconds after itleaves the preceding cell. In order to do this, a length or coil oftubing may be placed in the flow path in between the cells in order todeliberately introduce dead volume between the cells. An accumulationtank may also be used. However, an advantage of tubing, particular underone inch in diameter, is that tubing offers less mixing due to plugflow. Therefore, a volume of feed, concentrated or purified, solutionmay be fed into this excess tubing volume from one cell to the next withlimited cross contamination with a following stream of differentconcentration. The amount of tubing may be adjusted according to flowrate to accommodate sufficient dead volume in order to create a lagperiod of flow between cells of any length of time. This lag period isin order to give the subsequent cell to wash out its purified,concentrated, or feed water solution prior to triggering a rising ordeclining voltage cycle that initiates concentration or purification inthat cell.

Current Control

One advantage of a charge barrier cell is that conductivity may mirroror directly follow current. This may be used as a means of deliberatelycontrolling and monitoring output cell water purification orconcentration. For example, current, in amps, may be plotted versusconcentration or purification as measured by the conductivity meter inmilliSiemens or other units. This gives lines or curves of currentversus time, or of conductivity versus time, or versus voltage, for bothamperage and conductivity of the solution. These lines or curves may becurve fit and correlated to find an equation or constant slope, whichmay be used to interpolate or predict and/or control outputconcentration for any given amperage charging or discharging thecapacitor. The slope of the line may be used to program a logic deviceused to control product or wastewater output. For example, if waterconcentration surpasses or exceeds a desired set point, for example,more than 50% purified or more than 50% concentrated in relation to thefeed stream concentration, a logic means may utilize the above programor algorithm to regulate the output. For example, if it is desired tomaintain water product more than 50% purified, and the product fallsbelow this threshold, current through the capacitor, either dischargecurrent or charging current, may be increased. A steadily increasingcurrent may therefore be used in order to extend the cycle time withinwhich a desired water quality is produced. If water quality exceeds acertain threshold, current may be decreased based upon the aboveformula. This method works on the waste end as well as the purificationend, so that wastewater is not concentrated enough, current may likewisebe increased. If wastewater exceeds a desired threshold concentration,charge or discharge current through the capacitor may be decreased. Eachconcentration, fluid, and voltage may have its own formula and may bemeasured and preprogrammed. A capacitor system may contain a memorymeans in order to store this information for input into a program whichlearns from this information and uses it to control purificationfunctions. Purification and concentration cycles may lag, mirror, or beinverted from the current cycles. A lag may be caused by the deliberateintroduction of dead volume, accumulation or bladder tanks, or lengthsof tubing or pipe.

The charge curve need not contain a shunt cycle. Polarity may bedirectly reversed from a charged state.

Voltage Control

The charge barrier flow-through capacitor purifies or concentrates upona change in voltage. Unlike previous flow-through capacitors, a shunt, aperiod of time for a zero voltage cycle, is optional and not necessary.For example, it is possible to go from a minus voltage, through zero, toa positive voltage, for example, between −1.2 and 1.2 volts, withoutpausing at zero volts. This gives a triangular voltage cycle 54 thatcorrelates with a conductivity cycle 54. Conductivity 54 may be between0 degrees and 360 degrees out of phase with voltage 54.

FIG. 14 depicts such a charge barrier flow-through capacitor with such avoltage cycle. Voltage increase or decrease does not have to be linear.Alternatively, the change in voltage may follow any exponential,quadratic, logarithmic, elliptical, circular, trigonometric, sinusoid,or other mathematical formula. This formula may be programmed into andcontrolled by a logic means, which regulates the power and relays thatreverse polarity. FIG. 14 demonstrates purification upon a risingvoltage and concentration upon a decreasing voltage. Purification andconcentration are relative to a given feed stream, and may be, forexample, 10% to 90%, or 99% or greater, purification or concentration,and over two-fold concentration. The rate of change of voltage istypically more than 0.05 millivolts per second for purification, andtypically varies between −2 and 2 volts, or multiples of this for eachcell in a series stack. The rate of change of a particular individualcell voltage for concentration may be increased relative to thepurification rate of voltage change, for example, more than 1 or 2 timesfaster, in order to minimize wastewater.

To minimize energy and water losses, it is often important to rinse thewastewater from the flow-through capacitor of the present invention intowater at the same or higher concentration as the feed solution. However,this causes carryover of contaminated water. In order to allowpurification of more than 50% compared to the feed solution, the molaror mass ratio of wash or concentration cycle carryover ions per ionsremoved in a subsequent purification cycle must be less than 1. Apreferred means of achieving this is a charge barrier flow-throughcapacitor of the present invention with greater than 3 farads per eachmilliliter of dead volume. Dead volume is defined as thegeometrically-calculated volume taken up by all the flow channels andflow spacer within the charge barrier flow-through capacitor cell,cartridge holder, and any connecting tubes, tanks, or piping. Analternative method to eliminate ion carryover from concentration cycleto purification cycle is to use plug flow in order to wash the carryoverconcentration cycle out through the cell prior to a sequent purificationcycle. In order to do this, the flow spacers used are selected for goodrinsing properties with little carryover. Hydrophobic spacers, openchannel, or net spacers may be used. Alternatively, air may be used torinse out the cell between purification cycles. Excess wastewater mayalso be mechanically or hydraulically squeezed out.

Suitable means for performing logical functions, or logic instruments,are known to those skilled in the art, including without limitation:computers, processors, one or more communicating central processingunits, calculators, or instruments programmed or otherwise equipped toperform algorithmic or logical functions, or similarly equipped roboticsor human intermediaries.

The flow-through capacitors of the invention may be utilized in anysystem configuration common to ion exchange, electrodialysis, or reverseosmosis, or flow-through capacitors, including bleed and feed, batch, orcontinuous processes.

Flow-through capacitors, including the charge barrier flow-throughcapacitor of the present invention, may be configured as a removable ordisposable capacitor cartridge with the same cartridge and cartridgeholder geometries as any carbon block, microfiltration, reverse osmosis,or any other water filtration technology. Graphite or water-isolated,metallic electric lead means extend from the capacitor cartridge to orthrough the cartridge holder and thence to the electronics and powersupply.

EXAMPLES Example 1

The flow-through capacitor of FIG. 10 is prepared using electrodescomposed of 95% carbon black and 5% of a polymer PTFE or similarpolymer. Charge barriers are composed of permselective membranes. In thecapacitor of FIG. 10, a cation exchange membrane, such as RAIPORE™ 1010membrane with fixed benzyl sulfonic acid groups, is placed touching andadjacent to the negative electrode. An anion exchange membrane, in thiscase, a RAIPORE™ 1030 membrane with fixed phenyl tetramethyl ammoniumgroups, is placed touching and adjacent to the positive electrode. A0.003 inch thick filtration netting is placed between the twooppositely-charged permselective membranes and to form the flow path.The capacitor is charged at constant current, up to a voltage limit of 1volt. Seawater flowing between the membranes is purified to 12%. Inorder to reach a purity of 99%, several capacitors are used in series orstages with series flow to reduce the salinity to 6000 ppm. Anadditional flow-through capacitor, e.g., a reverse osmosis series stagemay be used to further reduce the remaining salinity to 250 ppm.

Example 2

The flow-through capacitor of Example 1 is used at a flow rate of lessthan 1 ml/minute/gram of carbon, for example, 0.1 mL/minute/gram ofcarbon, to achieve greater than 90% purification of a 35,000 ppm saltsolution.

Example 3

The flow-through capacitor of Example 1 is coupled through an inductorin order to recover energy during discharge. This energy is used tocharge a second capacitor during its purification cycle. Maximumcharging voltage of both capacitors is kept below 0.7 volts, in order tominimize energy usage. Capacitors may be charged either at constantvoltage, constant current, or at constantly increasing voltage, orconstantly increasing current. Optionally, capacitors may be charged inseries in, order to increase the voltage for maximum energy recovery andpower supply efficiency.

Example 4

The flow-through capacitor of FIG. 11 is made by using activated carbonblack as the electrodes. A low RC time constant material, such as carbonfibers, nanotube mesh, or low capacitance activated carbon cloth aerogelis used as a charge barrier material. Water with 5000 ppm minerals andsalts is passed through this device at a flow rate of less than 20ml/minute per gram of carbon, with the flow rate adjusted downwards inorder to achieve 95% purification. The flow rate may be furtherdecreased into the charge cycle in order to maintain the desired levelof purification for a longer period of time. Once the level ofpurification drops below 80%, the capacitor is discharged through anenergy-recovery circuit. That energy is added to the energy from the DCpower source and used to charge another capacitor which purifies whilethe first capacitor is releasing a concentrated stream of contaminants.

Example 5

The flow-through capacitor of Example 4 may be powered by a fuel cell.

Example 6

A flow-through capacitor is made utilizing low surface area carbonblack, in the range between 300 and 900 Brunauer Emmett Teller method(B.E.T.), selected for being less likely to passively adsorbcontaminants and therefore foul the flow path. The charge barriermaterials are NEOSEPTA®. The flow arrangement is a dual-flow channeldevice as shown in FIGS. 7 and 8A, 8B, 8C, and 8D. One flow channel isformed between and by spacing apart the two charge barrier materials. Apair of side flow channels is located on either side of the central flowchannel. These side flow channels are also formed by placing a spacerbetween the electrodes and the charge barrier materials. A membrane thatselectively allows anions to migrate through it (anion permselective,because it has bound positively-charged ionic groups), is initiallyplaced on the side of the negative electrode, with a flow spacer inbetween. The membrane that selectively allows cations to migrate throughit (cation permselective, because it has bound negatively-charged ionicgroups). During this charge cycle, purified water is retrieved from theoutlet of the central flow channel. Simultaneously, concentrated wateris retrieved from the electrode facing side flow channels.

The same flow-through capacitor may subsequently be discharged. Aconcentrated solution is recovered from the central flow channel. Thecapacitor may be repeatedly run in this polarity sequence.Alternatively, the polarity may be reversed. Reversing the polarityplaces the permselective membranes adjacent to the oppositely-chargedelectrodes. This means that a concentrated stream is recovered duringthe charge cycle from the central flow channel. Simultaneously, apurified stream may be recovered from the side flow channels.Subsequently, the flow-through capacitor may be discharged. During thedischarge cycle, a purified liquid is recovered from the central flowstream, and a concentrated liquid is recovered from the side flowchannels.

Example 7

A flow-through capacitor is made utilizing one micron small particlesize activated carbon powder electrodes bound together with 5% PTFEbinder. The charge barrier material is a conductive polymer coating0.001 inch thick. Ten of the charge barriers are connected in a 7-voltseries bank of capacitors. Seawater of 35,000 ppm is treated to 500 ppmat an energy usage of 0.7 joules per coulomb. 70% of the energy isrecovered during discharge of the capacitors using inductive coils torecharge a second bank of capacitors in series.

Example 8

In a flow-through capacitor using edge plane graphite with a surfacearea of 500 square meters per gram for electrodes, an anion and a cationexchange membrane are used as charge barriers. An additional pair ofbipolar membranes is placed between the cation or anion membranes andthe electrodes. Flow spacers are placed between all the above layers, ormerely between the cation and anion exchange membranes. The resultingcell may be used in any application of bipolar membrane electrodialysis,but without oxidation reduction reactions at the electrodes, forexample, recovery of organic acids, proteins, or biological moleculesfrom fermentation broths. Another application is the recovery of SO² orNO³ from stack gas.

Example 9

A flow-through capacitor is made using an electrode composed of ahigh-capacitance electrode material, such as high-surface-area carboncloth, or edge plane graphite, or carbon black particles bound togetherwith fibrillated PTFE. Membranes selective for transmigration of cationsand anions, respectively, are placed touching the electrodes. A centralflow channel is formed by any spacing component, including biplanarfiltration netting under 0.01 inches thick, screen-printed protrusionsor ribs, or membranes textured with premanufactured flow channels in adiamond pattern. The initial charge sequence is at constant currentselected for low I squared R energy losses, where “I” is amps and “R” iselectrical series resistance. A top charging voltage of 0.6 volts isselected to minimize the amount of energy required to purify a givenamount of ions. The charge cycles are carried out as follows:

During the first charge cycle, the electrodes are of the same polarityas the fixed charge inside the membranes. Coions expelled from the porevolume of the electrodes are trapped against the membranes. This causesan amount of counterions in the central flow channel to migrate throughthe membranes, where they form a concentrated solution in the electrodelayer. This counteracts the losses ordinarily caused by adsorption andexpulsion of dissolved pore volume salts. Therefore, the ionicefficiency, as measured by coulombs of ionic charge purified divided bycoulombs of electronic charge utilized, is greater than 30%. In thiscase, for 35,000 ppm salts, ionic efficiency is 85%, and the energyutilized is 0.35 joules per coulomb of charge.

The next cycle is a discharge cycle in which concentrated waste isreleased into a feed stream fed into the central flow channel andrecovered from the outlet. The next cycle, after discharge, is a reversepolarity charge. Here, the bound charge on the membranes is opposite tothe electronic charge on the electrodes. Ions are driven from theelectrode across to the adjacent membrane, but cannot migrate throughthe second membrane. Therefore, a concentrated solution forms in thecentral flow channel and is released through the outlet. Upon dischargefrom this polarity, ions migrate from the central flow channel back intothe electrode chambers, thereby purifying the feed stream. Thesubsequent cycle goes back to the beginning. These cycles can berepeated as many times as desired. An example of data from the above isshown in FIG. 9. FIG. 9 shows the underlying usefulness of the chargecycle in Example 7. Note that two purification cycles occur in a row.Likewise, two concentration cycles occur in a row. This doubling up ofpurification or concentration artificially extends the length of timethe capacitor is performing a particular purification or concentrationcycle.

Example 10

The flow-through capacitor of FIG. 11 is used to make ultrapure waterof, e.g., 18 megaohms cm. The water may be pretreated using one or moreof a microfilitration unit, a water softener, and followed by a reverseosmosis unit. The water may be post treated using, e.g., a polishing bedof deionization resin. The flow-through capacitor removes some or all ofthe dissolved solids from the deionization bed, thereby prolonging thelifetime of the deionization bed.

Example 11

The flow-through capacitor of FIG. 11 may be used to post-treat seawaterwhich has been previously treated by reverse osmosis. The salinity ofthe seawater is initially reduced by reverse osmosis from 35,000 ppm to10,000 ppm. Subsequently, treatment with the flow-through capacitorfurther reduced the salt concentration to 250 ppm. The combined use ofreverse osmosis and the flow-through capacitor desalinated seawater for15 kw hours per thousand gallons, which is a 30% energy savings comparedto using reverse osmosis alone.

Example 12

The flow-through capacitor of the invention may be used to purifyseawater to 500 ppm.

Example 13

Individual flow-through capacitor cells are made with the followingsequence of layers: current collector layers, such as using 0.005 inchthick graphite foil; an electrode layer of any capacitance material, forexample, carbon microparticle containing sheet material; a pair ofcharge barrier layers consisting of carbon cloth or of an anion and acation exchange membrane bracketing a central flow netting spacer of0.005 inch thick polypropylene; a second electrode layer needed to forma pair; and a second current collector layer. The current collectors areionically insulating but electronically conductive. Therefore, if anumber n of the above sequence of layers are stacked up as flat sheets,or rolled in concentric spirals, they will form a series-connected,flow-through capacitor with single-sided capacitive electrodes facingoutwardly from the current collector. The current collector forms theionically-nonconductive boundary between cells and establishes anelectrical series connection. If the electrode is conductive enough notto require a current collector, then a thin sheet of plastic may be usedas long as series leads are connected between cells. The electrode doesnot need to be single-sided. Any number of double-sided electrodesconnected electrically in parallel may exist within particular cells.Each cell may be made with the same capacitance by matching theconstruction of each cell. Flow in the spiral cell may be alongside thelayers.

Example 14

Activated carbon particles in the 0.2 to 5 micron diameter range,conductive ceramic, aerogel, carbon black, carbon fibers, or nanotubeswith a BET of between 300 and 2000, are mixed together with 5% PTFEbinder, ion exchange resins as a charge barrier, andcarboxymethylcellulose as a plasticizer, and calendered into a 0.01thick sheet. These are made separately in anion, cation, and bipolarversions. Any ion exchange resin known to be used in ion exchange orelectrodialysis membranes may be used. Ion exchange groups include anystrong or weak acid or base, for example, sulfonic acid or amine groups.Ionic group support material includes any material used in ion exchangeor membranes, including fluorinated polymers, divinylbenzene, or styrenepolymers, or any other kind of polymer, zeolite, or ceramic material.The geometry of construction will be known to those of skill in the art,including, but not limited to those described in the U.S. Pat. Nos.5,192,432, 5,415,768, 5,538,611, 5,547,581, 5,620,597, 5,748,437,5,779,891, and 6,127,474, each hereby incorporated by reference in itsentirety. The electrodes may be spaced apart or provided with a flowspacer and an optional current collector in order to form a chargebarrier flow-through capacitor. The advantage of this example is thatthe charge barrier material is evenly distributed throughout theelectrode layers, thereby eliminating extra charge barrier layers, thecost due to these extra parts, and allowing the electrodes to be spacedcloser together, less than 0.02 inches, for example, which cutsresistance and increases flow rate of purification. Monolithic orsintered carbon electrodes may also be used, for example, electrodeswith honeycomb holes incorporated into the structure may have theseholes filled in with ion exchange resin to effect a combined chargebarrier electrode material.

Example 15

In one embodiment, a charge barrier flow-through capacitor may beprepared as follows:

Pairs of carbon electrode material consisting of a fibrillateable PTFEcarbon powder mixture in the ratio of under 5-15% PTFE, and 95-85%carbon is used as an electrode. The powdered carbon is any highcapacitance carbon with a single electrode capacitance of over 10 faradsper gram as measured in 0.6 M KCL, for example, activated carbon powderwith particle size less than 100 microns and surface area of 1000 squaremeters per gram as measured by the B.E.T. method. The end electrodes maybe single-sided. Intermediate electrodes may be double-sided, may have asingle side of high capacitance material and a side of graphite currentcollector, which may be made with open area more than 10%, openings orpores to facilitate ion transport through the current collector so thations conduct into both sides of the high capacitance layer, or, highcapacitance layers may be on either side of an optional currentcollector, such as a layer of graphite. This layer of graphite may beapplied with a binder and integral with the electrode, or be a separatepiece of graphite foil, for example, under 0.020 inches thick. Graphitemay be easily mixed with a binder and directly applied to carbonelectrode sheet material via rollers, doctor blades, spraying, or anycoating method directly onto the carbon electrode in order to form anintegral current collector. If necessary, binders are sinteredsubsequently or heat-treated in order to cure or drive awaynonconductive or toxic components.

A single polarity charge barrier material in contact with one of thepair of electrodes form the anode and cathode layers of the capacitor ofthe present invention. In this example, a porous polymer or polyolefinmembrane with acrylic acid, amine, sulfate, chelating, azide, cynanide,carboxyl, super absorbent polymers, surfactants, any cationic, anionic,zwitterionic groups, including sulfonic acid, quaternary amine, amine,phosphate, cynanide, or trimethylbenzylammonium groups.

For single-sided charge barrier flow-through capacitors, layers ofmaterial may be put together in the order of electrode, charge barrier,flow spacer, and electrode. A double-sided charge barrier capacitorincludes an extra charge barrier layer of the same or opposite polarityfrom the first, placed between electrode layers. All layers may berepeated any number of times. Electrodes may have an optional currentcollector and be single or double-sided with the current collector inthe middle of two carbon sheets. A flow spacer is optional and may beany net, woven, melt-blown, spun-bound, nonwoven, or particle material,preferably less than 0.03 inches thick. One preferred embodiment is toeliminate a separate flow spacer and to form the flow channel 5 shown inFIGS. 2 and 15 by texturing either one or both of any two facing layers,for example, an electrode and charge barrier layer, two electrodelayers, or two charge barrier layers. Grooves may be made directly intoeither of these layers. When one or two grooved electrodes, electrodeand charge barrier, or double charge barrier layers are placed togetherwith the grooves offset at an angle, biplanar flow channels form as aresult. This eliminates a separate flow spacer layer, decreased distancebetween electrodes to under 0.03 inches, and thereby eliminateselectrical series resistance to under 150 ohms cm² as measured in 0.6 MKCL. The cm² above refers to the total facing area between all theelectrodes.

The above layers may be laminated together in order to integrateelectrodes with charge barriers and flow spacers. Charge barriers andcurrent collectors may also be used to form gaskets in order to separatemultiple or single electrode electrical series cells. A nonconductivesheet material, 53 in FIG. 15, may similarly be placed between numbersof electrode layers in order to electrically isolate series capacitors.Material 53 may be a plastic or polymer sheet material or any ionicallyand electrically-insulating material. Electrical insulator material 53may be used, in double as well as single-sided charge barrierflow-through capacitors. If similar lengths or amounts of electrodematerial are used in each series cell, voltage will divide evenlybetween the cells in the series stack. A series stack may be formed byspiral-winding equivalent amounts of material per series cell. Each cellin the series will be formed in a concentric manner around a centralaxis or spindle. In cross section, each series cell may need to form athinner concentric layer in order to maintain a similar amount ofmaterial per cell as the radius of the cylinder increases. The ends ofthis spiral-wound series cell may be sealed completely with resin ormechanical means, leaving inlet and outlet holes for flow paths into andout of the each end for each cell, or, the ends may be placed less thanone-half inch away from a cartridge holder or end plate, in order thatthe electrical flow path between series cells is over one ohmresistance, while maintaining parallel fluid flow paths. Alternatively,flow path may also be in series, in which case, flow may be serpentinefrom one cell to the next.

It may be desirable to manufacture series cells of up to twenty cells inseries. These series cells may be in turn grouped together into higherseries totals. Electronic monitoring and control means may be insertedbetween each series cell stack or group in order to ensure that voltagescontinue to balance within 50% from cell to cell, preferably within 10%.It is also desirable to manufacture series cells with multiple leadsfrom each cell, so that the cells may be individually shunted andbrought to zero volts.

Example 16

A charge barrier flow-through capacitor is used with a solution of over10 ppm at a flow rate of less than 5 ml/minute/gram of carbon to as lowas 0.1 ml/min/gram carbon in order to obtain a product solution of 90%to more than 95% purified at a voltage of voltage which varies between−1 and +1 volt every 1000 seconds or less, or less than 1 millivolt persecond. If desired to achieve low wastewater, the voltage variationduring the concentration part of the cycle may be increased to change ata rate of more than 1 millivolts per second. Purification orconcentration may be upon either a rising or a falling voltage,depending upon the polarity of the cell or power supply connected to thecell.

1. A method of deionizing a fluid, said method comprising: (a) allowinga fluid containing ions to flow through a flow channel in fluidcommunication with at least two electrodes, wherein at least one of saidelectrodes comprises a pore structure such that said electrode is aporous electrode having a pore volume containing pore volume ions; (b)applying a voltage to said at least two electrodes to form a firstelectric field between said electrodes, whereby at least one of saidelectrodes has a capacitive charge; (c) allowing electrostaticabsorption of ions from said fluid in said flow channel by saidelectrodes in said electric field, and allowing said porous electrode toexpel at least a portion of said pore volume ions; and (d) allowing asecond electric field, inverse to said first electric field, to existbetween said flow channel and said porous electrode, whereby saidexpelled pore volume ions are retained within said second electricfield.
 2. The method of claim 1, wherein said allowing a second electricfield to exist comprises the step of allowing said second electric fieldto form.
 3. The method claim 1, further comprising the step ofmonitoring the concentration of ions in a fluid in said system.
 4. Themethod of claim 1, wherein said method alternately comprises chargecycles and discharge cycles.
 5. The method of claim 4, wherein saiddischarge cycle comprises a shunt between said electrodes.
 6. The methodof claim 4, wherein said discharge cycle comprises reversing said firstelectric field.
 7. The method of claim 6, wherein said method furthercomprises reversing said second electric field.